The central element in a fluorescent lamp is a sealed glass tube. The tube contains a small bit of mercury and an inert gas, typically argon, kept under very low pressure. The tube also contains a phosphor powder, coated along the inside of the glass. The tube has two electrodes, one at each end, which are wired to an alternating current (AC) supply.
When you turn the lamp on, current flows through the electrical circuit to the electrodes within each end of the fluorescent tube. Considerable voltage is developed across the electrodes and electrons migrate through the gas from one end of the tube to the other. This energy changes some of the mercury in the tube from a liquid to a gas. As electrons and charged atoms move through the tube, some of them will collide with the gaseous mercury atoms and these collisions excite the atoms, bumping electrons up to higher energy levels. When the electrons return to their original energy level, they release light photons creating light.
Phosphor coatings are provided within fluorescent tubes to give off light when they are exposed to light. In a fluorescent lamp, the emitted light is in the visible spectrum—the phosphor gives off white light we can see and manufacturers can vary the color of the light by using different combinations of phosphors.
The testing of fluorescent lamps is typically done through randomly replacing lights within ceiling mounts. This can lead to over sampling light tubes to determine an operating state of each light bulb which may take a considerable amount of time. As such, what is needed is a method and apparatus for testing a fluorescent tube without mounting a fluorescent tube within a light fixture to determine its operational status.